The present invention described herein relates to the field of density measurement. More specifically, the invention relates to devices and techniques using radioactive decay to measure density. The invention especially relates to alpha particle densitometers.
Frequently, the density of very thin materials or gases, such as air, must be measured automatically to a high degree of accuracy. This requirement is particularly desired in an airborne vehicle for which a measurement of air density is employed for the calculation of air pressure. Radioactive particles may be employed to determine air density since particles from a particular radioactive source have a discrete energy and a predictable distance of decay from the source in a medium of a particular density such as air.
A radioactive source has a specific half-life whereby the source is constantly undergoing decay. Since a particular radioactive substance that emits alpha particles is constantly decaying with time, the number of alpha particles which are emitted varies as a function of time thus requiring calibration of the emission of alpha particles at appropriate time intervals in order to measure density accurately. Thus, it would be desirable to provide an alpha particle densitometer that compensates for the fact that the alpha particle source undergoes constant decay.
Still other radioactivity-based methods for measuring the density of low density materials, such as air, require calibration at periodic intervals. Similarly, it would be desirable, in general, to provide a radioactivity-based densitometer that does not require periodic calibrations due to the decay of the radioactive substance and that compensates for that decay.
Other radioactivity-based methods for measuring the density of air use beta particles, and these methods are not very accurate. It would be desirable to have a very accurate method for measuring air density.